Dressed in a navy blue Naeem Khan gown at UNICEF’s Snowflake Ball on Wednesday, Katy Perry told US Weekly that she left an important part of her ensemble at home: her shapewear.

“I feel like my [fat] is sticking out so bad right now. I almost always wear [Spanx], but not tonight, and I feel it pushing out, making me look fat. … I like to say I run on the elliptical for 30 minutes watching CNN, but I don't do it often enough. So I'm just like, ‘Oh, I guess I'm not fitting into this Lanvin dress for these couple of months.’ ”

Despite her missing undergarment, the pop star looked radiant walking the blue carpet at the New York City event.